i don't know much on psi vampires, but if you feel this way, work on shielding. start by charging yourself with positive white energy and releasing all negative dark energy. you can do this while meditating, or try a sea salt bath, let the water purify you. once you're ready visualize a shield of white/silver light surrounding you. you might have to visualize or think of it throughout your day for the first little while to remind yourself it's there. this along with the charging should be done daily to keep it strong and clean. making a protection charm and wearing it will also help.
for your ex friend, if she is bothering you, simply bringing it up to the teacher or principal could help if she's threatening you and stalking you, but if it's just you're in the same class together leave it. a banishing spell could keep her away from you. a binding spell is designed to keep her close... unless you were trying to bind her to a locker or something.